In recent years, fuel cells have attracted attention as power supply devices for mobile electronic devices such as personal computers (PCs) and personal digital assistants (PDAs). The fuel cell generates electric power using hydrocarbon-alcohol fuel. More specifically, the fuel cell generates electric power by an electrochemical reaction between hydrogen from alcohol and oxygen from the air. Accordingly, if an electronic device is provided with a fuel cartridge filled with alcohol fuel, electric power can be generated on-site regardless of the presence of an alternating current (AC) power supply.
Compared to secondary batteries such as lithium ion batteries, the fuel cell outputs less electric power per unit of volume. That is, to generate all electric power consumed by an electronic device, the fuel cell need to be large. In view of this, Japanese Patent Application Publication (KOKAI) No. 2009-124858 discloses a conventional technology related to a power supply device. According to the conventional technology, the power supply device monitors the use state of a mobile electronic device. According to the power consumption of the electronic device, the power supply device uses a fuel cell or a secondary battery to supply electric power to the electronic device.
With the conventional technology, the timing of switching between charge and discharge of the battery is not managed. Therefore, the battery is not switched from discharge mode to charge mode when its remaining charge allows it to be efficiently charged, resulting in inefficient charge/discharge cycles of the battery. Besides, since the remaining charge of the battery is not taken into account to switch between charge and discharge of the battery, the life of the battery may be reduced due to excessive charge and discharge.